Preheat oven to 350F.
In a bowl, combine flour, salt and pepper. Add beef; shake to coat evenly. In a Dutch oven or large heavy pot, Add half the beef to pot, shaking off any excess flour. Cook, stirring occasionally, until browned. Remove beef with a slotted spoon. Repeat with remaining beef. Add the onions to the dutch oven and toss to coat in the fat. Saute, stirring occasionally, until soft, 5-6 minutes. Add garlic; sauté, stirring constantly, until fragrant, 1 minute. Add the tomato paste and work into the vegetables.
Deglaze the pot with the balsamic vinegar, stirring up the brown bits from the bottom of the pot, until the vinegar stops bubbling and is mostly evaporated, 1-2 minutes. Return the browned beef to the dutch oven. Pour in enough broth to barely cover the beef (about 3 cups), wine, as well as salt and pepper. Give everything a good stir. All the liquid to come to a simmer.
Cover the pot, turn off the burner and transfer to the oven. Braise for 1 hour. Add the chopped potatoes, carrots, and squash. Cover and return the stew to the oven to continue braising. Braise an additional 1-1.5 hours, or until the beef is falling apart and the vegetables are tender. Test for doneness around the 1 hour mark. Add in the peas and serve hot.
